Maternal characteristics impact the relationship between fetal sex and superimposed preeclampsia

Associations between female fetal sex and preeclampsia occurring preterm have been reported but data is inconsistent across populations. We explored if the relationship between fetal sex and various hypertensive disorders of pregnancy (HDP) is modified by maternal characteristics.

We conducted a retrospective cohort study analyzing data from 43,737 singleton pregnancies. A modified Poisson regression model with robust error variance was used to calculate relative risk (RR) and 95% confidence intervals (CI) for the association between female fetal sex and HDP.

Models were adjusted for maternal age, smoking, body mass index, and gravidity. Relative excess risk due to interaction examined interaction between maternal characteristics and female fetal sex, on risk of HDP.

Female fetal sex was marginally associated with superimposed preeclampsia (RR_adj. 1.13, 95 % confidence interval [CI] 1.00 - 1.28) but no other associations were observed. There was interaction between female fetal sex and advanced maternal age (>35 years), obesity, and parity. After stratifying by these variables, those with a female fetus and advanced maternal age had an increased risk of superimposed preeclampsia (RR_adj. 1.29, 95 %CI 1.05-1.58). We observed a similar trend among parous (RR_adj. 1.15, 95 %CI 1.00-1.34), foreign-born (RR_adj. 1.20, 95 %CI 1.00-1.44), and obese (RR_adj. 1.27, 95 %CI 1.03-1.35) individuals.

Female fetuses may respond differently to underlying maternal characteristics influencing risk of superimposed preeclampsia, but no other associations were observed.